The detective work, both on what it is and where do i get what I need starts here.
First up, closer inspection of the engine numbers may show them to match, but for sure they aren’t original Yamaha numbers, Not-so subtle use of a file and poor aim with the number punches show the numbers on the bike ‘3(or 5)15341045’ not to be related to any known Yamaha. Ah.
There’s a good article with the Yamaha dirt bike engine number ranges which show that Yamaha 250 MX bikes should have the following ranges.
| Model | Year | starting engine number |
| MX 250 | 1973 | 364-000101 |
| MX 250A | 1974 | 364-020101 |
| MX 250B | 1975 | 509-000101 |
So working out what year specifically the bike (and which model it is) becomes a little more tricky and I’ll have to look for subtle differences, if there are any.
The CycleChaos – wiki site has some good pictures of the MX250, A and B where the 1975 B model is actually a monoshock. This narrows it down a bit, so the bike is either a 73 or 74 model and for both the exhaust system and cycle parts seems to be similar, just the plastics and paint-work being different (I think).
Looking for Parts
The search for parts and a strip down of the bike begins here:
– airbox, its missing
– wheels, spokes and rims. Both rims look well bashed so may need replacing if they can’t be straightened.
– front brake, missing front brake arm. Also need to look out for brake shoes.
– mudguard / fenders [[already getting use to the language changes for search ebay.com]], none on the bike, some choices here including some YZ copies in yellow available in the UK, they’ll look the closest.
– sidepanels, none
– tank, need some decals for the tank, when its resprayed and filled
– chain & sprockets, the sprockets look ok but may need to be replaced.
The good thing about Yamaha’s is that there are lots of parts to choose from and availability is pretty good. Also, although the MX was never a UK bike, you would hope that lots of the bits from the DT (which was a UK bike) should fit. Anyway, the search and ordering starts here.
|Airbox|Ebay is going to be the place, as its a deleted item on the Yam spares list |The fibreglass airbox will be a challenge, though there is one on ebay in the US, will look for local options|
|Brake Shoes|Based on a US listing for a pair of Yam brake pads, DT250, 400 (and lots of other models) fit|Ordered from Yambits on ebay UK|
|Cables|They all need replacing| Venhill website doesn’t list specific MX cables, but either DT or universal cables should fit |
|Chain|Should be a 520 – 106 chain, can get that locally|LG Racing are local |
|Controls|Not so worried about originals| Again, will look at LG Racing |
|Electrics|All look ok, including the CDI and cabling.| |
|Fork Seals|Will need replacing|Like the head bearings, from ebay and p.k.n |
|Handlebars|Looking for some original looking bars|Found some reasonably priced chrome bars from Yuniparts |
|Manual|There’s a Clymer 68-76 Dirt Bike Manual and I think a Haynes Trail Bike alternative|Couple of download options, but I’m a fan of the real thing. Will see what’s on ebay US|
|Plastics/Mudguards/Side Panels|Will look at pattern options from UK and US|Yuniparts in UK do a yellow front, but not rears. Reproduction Decals in Canada do all the plastics for the 73 and 74 MX250’s|
|Steering Head Bearings|These are originally ball bearing races and need replacing the more modern taper roller bearings|Listed on ebay and are from Pyramid Parts in the UK |
|Seat Cover|Replacement covers available in the US and er. Thailand|Ordered from Pit Replica ebay shop in the US, from Thailand, so we shall see|
|Shock Absorbers|Could go for a shock rebuild, or a new set| see table below|
|Tank Decals|Harder than I thought|There are some NOS decals on Speed and Sports extensive spares list for Yamaha dirt bikes, but maybe not a $60.00|
The hunt continues for the other parts and the bike strip-down is also happening
Did some shock absorber research….
|Falcon | List a fitment for the MX 250 , but at GBP 190 for the steel and nearly £300 for the aluminium bodies, there not cheap |
| NJB | Offer clubman and expert scrambles shocks |
| Road and Race Suspension | Offer a twinshock rebuild service though the OEM shocks on the MX aren’t rebuildable AFAIK |
| Betor | MX and Enduro shocks Got these on a couple of trials bike and whilst ok, aren’t stunning. Haven’t tried the newer Aluminium version |
Decision in the end, after speaking to Norman Blakemore on the phone at NJB Shocks was to go for the expert scrambles shocks, at GBP 103. They are 330mm, so just over the original 320mm.. Will keep you posted on performance.